This invention relates generally to the treatment of sewage. More particularly, this invention relates to the treatment of sewage discharged from houses and other buildings which are not connected to a municipal sewer system such that, after the sewage has passed through the diffusion bar aerobic treatment plant (xe2x80x9cDBATPxe2x80x9d), it has been cleaned to a level acceptable for discharge directly into the environment so that it will not contaminate the ground water. Thus, the DBATP provides an alternative to septic systems for buildings constructed outside of a local municipal sewer system.
While there are several different existing types of conventional sewage treatment devices available for use with buildings located away from municipal sewer lines, the DBATP offers a single, simple-to-install unit comprised of three tanks, which provides a more comprehensive cleaning process than previously known in the art field. The DBATP uses a three step cleaning procedure. First, the sewage enters a pre-tank, in which trash items are trapped, gravity separation of solids from the effluent begins, and anaerobic microorganisms initially break down the sewage. Then, in the aerobic tank, air is injected into the sewage using a diffusion bar device to stimulate the growth of aerobic microorganisms, which further process the sewage, cleaning the effluent more thoroughly. The design of the diffusion bar of the present invention encourages the dispersion of smaller micro-air bubbles throughout the sewage in the aerobic tank, so that oxygen entrainment is increased in order to maximize the effectiveness of the aerobic microorganisms cleaning the sewage. Finally, the post-tank acts as a clarifier, so that the effluent is progressively cleaned by gravity separation in order to remove any solid particulate matter. Through this multi-step process, the DBATP produces a clean, environmentally-safe effluent using one, easily-installed device.
The DBATP is a device utilizing a multi-stage procedure for treating and cleaning sewage. The DBATP is typically a single unit comprised of three separate tanks: a pre-tank (also known as a trash tank), an aerobic tank (also known as a mixing chamber), and a post-tank (also known as a clarifier). The pre-tank holds the sewage for a time while allowing the anaerobic microorganisms in the sewage to begin initially breaking down the sewage. The pre-tank also acts to capture trash items and to prevent them from progressing through into the aerobic tank. Some initial gravity separation of solid particulates suspended in the sewage effluent also begins while the sewage is being held in the pre-tank. The aerobic tank houses the diffusion bar, through which air and/or oxygen is distributed into the sewage. The injection of air and/or oxygen into the aerobic tank stimulates the growth of aerobic microorganisms. The aerobic microorganisms (primarily bacteria) break down the sewage further as they digest the contaminants in the effluent, and this is the primary sewage cleaning stage of the DBATP. The post-tank acts as a clarifier or settling chamber, in which gravity separation occurs, filtering out solid particulates from the cleaned effluent, so that only cleaned effluent is discharged from the post-tank. Generally, all three tanks are joined together into a single unit, allowing for a compact device which can be conveniently installed. A compact, unitary device is useful since these types of sewage treatment devices are typically installed below ground, buried in a yard for example. Thus, a compact device requires less digging effort and less damage to the yard during installation.
The raw sewage enters the pre-tank first to allow the anaerobic microorganisms in the sewage to begin the initial processing of the sewage. The pre-tank has side walls, a top, and a bottom. Anaerobic microorganisms feed on the sewage, breaking it down in the process. The pre-tank also serves to screen out objects which would hamper the functioning of the aerobic tank. As the pre-tank continues to accept raw sewage, sewage is forced out of the pre-tank through the outlet conduit. Typically, the outlet conduit is an overflow conduit located near the top of the pre-tank which leads to the aerobic tank. Gravity will segregate the sewage in the pre-tank, such that light solids will float upon the surface while heavy solids will settle to the bottom. In between these two zones is a zone of effluent which is relatively free of particles. The overflow conduit drains sewage from this particle-free zone beneath the surface level, thereby screening out floating solids and heavy solids. An effluent filter, which is not required, may cover the opening of the overflow conduit to further prevent large particles from passing through the overflow conduit. In this way, the overflow conduit traps the large solid contaminants so that they do not enter the aerobic tank, where they might interfere with the aerobic treatment process by affecting the dispersion of oxygen throughout the sewage. The overflow conduit also reduces the chances that the DBATP will become clogged. After the raw sewage has been gravity separated and processed by anaerobic microorganisms, it flows into the aerobic tank for the next stage of the treatment process.
The aerobic tank is a vessel with sidewalls, a top, and a bottom. It encompasses a diffusion bar mechanism which is connected to an external pump/compressor so that it emits air bubbles into the sewage in the aerobic tank, aerating the sewage in order to facilitate the growth and activity of aerobic microorganisms. Aerating the sewage activates and stimulates the aerobic microorganisms in the sewage. This causes the aerobic microorganisms to multiply and increases the amount of sewage that they digest. Air bubbles emitted from the diffusion bar also act to stir the sewage in the aerobic tank, mixing the sewage so that oxygen is distributed throughout and so that there are no dead zones which could reduce the effectiveness of the aerobic process. The turbulence caused by the bubbles also prevents build-up on the walls of the aerobic tank, so that the walls are kept relatively clean. The turbulence of the air bubbles also helps to break down solid particulates within the sewage, so that the aerobic bacteria can more effectively clean the sewage.
Typically, the diffusion bar is comprised of hollow tubes. Although a variety of configurations and arrangements are possible and would produce a functional diffusion bar, the preferred embodiment utilizes a T-shaped air feed tube, which brings air from the aerator pump (compressor) outside of the tank, and two generally vertical aerator tubes, which disperse air into the sewage. The aerator tubes are conduits which each have holes drilled in them through which air can flow, and the bottom of each aerator tube is generally capped, forcing any air pumped into the diffusion bar to exit through the holes in the aerator tubes. Thus, air will bubble out of the diffusion bar into the sewage in the aerobic tank. In the preferred embodiment, the diffusion bar also includes two deflector plates, one located near the top of each aerator tube, above the holes. As air exits the holes in the aerator tubes of the diffusion bar, it bubbles quickly upward in a nearly vertical line near the aerator tube from which it exited. These air bubbles will smash into the deflector plates located above the holes, bursting into smaller bubbles which will increase the amount of oxygen entrainment in the aerobic tank.
The deflector plates are designed to break down the bubbles emitted from the holes in the aerator tubes, producing smaller bubbles. Smaller bubbles and increased oxygen entrainment help to increase the efficiency of the aerobic bacteria (since there is more air bubble surface space upon which the bacteria may act), such that the aerobic cleaning process produces better results. The deflector plates also act to disperse the bubbles outward away from the diffusion bar, so that oxygenation is better accomplished, and to increase the turbulence within the sewage in the aerobic tank, improving the mixing effect. This ensures better aeration of the sewage throughout the aerobic tank, and a more uniform cleaning process. In all of these ways, the deflector plates on the diffusion bar improve the operation of the aerobic tank, producing a cleaner effluent.
Although the diffusion bar in the preferred embodiment is Y-shaped, with two vertical aerator tubes attached to the ends of a T-shaped air feed tube, this shape is not necessary. The critical feature of the diffusion bar is simply that it disperses air through holes located near the bottom of the aerobic tank. Furthermore, the location of the diffusion bar, away from the separator wall between the aerobic tank and the post-tank (and in the preferred embodiment, adjacent to the wall between the aerobic tank and the pre-tank), is important to direct the sewage towards the post-tank (which acts as a clarifier), to oxygenate the sewage as it is introduced into the aerobic tank (for maximum aerobic processing time), and to cause maximum turbulence within the sewage as it initially enters the aerobic tank, with the sewage becoming more calm as it approaches the post-tank (thereby encouraging settling and gravity segregation in the post-tank). When deflector plates are used to improve the efficiency of the diffusion bar, the critical factor is the location of the deflector plates with regard to the holes in the diffusion bar: a deflector plate should be located a slight distance above the holes in the diffusion bar so that the rising air bubbles will collide with the deflector plate.
The post-tank is a vessel with sidewalls, a top, and a bottom. The sidewall between the aerobic tank and the post-tank, however, does not completely separate the two tanks. Rather, there is a gap (which is several inches high and which typically spans the entire width of the tanks) along the bottom of the tanks, so that effluent can flow from the aerobic tank into the post-tank underneath this separator wall. Thus, the wall between the aerobic tank and the post-tank hangs down but does not touch the bottom of the tanks, and acts more as a separating baffle than as a structural support element. By design, the post-tank acts as a clarifier. The bottom of the post-tank slopes upward as it move away from the aerobic tank. Located near the top of the post-tank is an outlet, where the cleaned effluent is discharged to ground. The post-tank is a zone of relative calm, since the separator wall shields the post-tank from the turbulence of the aerobic tank. As the sewage is pushed into the post-tank and up the sloped bottom, gravity separation occurs, with heavy particulates falling out of the effluent as it rises up in the post-tank. As the effluent progresses up through the post-tank, contaminants in the effluent are continuously acted upon by gravity, and will settle towards the bottom of the post-tank. In this way, the post-tank acts as an effluent clarifier, screening out solid contaminants so that the effluent at the top of the post-tank, which is discharged to ground through the outlet, is clean and relatively free of solid particulates.
It is an object of this invention to clean sewage in preparation for discharge. In doing so, this invention captures trash in the pre-tank, uses both aerobic and anaerobic microorganisms to break down the sewage, and utilizes gravity separation to clarify the effluent for discharge. It is still another object of this invention for it to be easy to install, durable, and to require little maintenance. It is yet another object of this invention to provide for a multi-stage cleaning process using three tanks in a single, compact unit. It is yet another object of this invention to discharge water which meets or exceeds state water quality requirements. It is yet another object of this invention to increase the effectiveness of the aerobic treatment of sewage by utilizing a diffusion bar design which increases aeration and oxygen entrainment. It is yet another object of this invention to improve aeration throughout an aerobic tank by utilizing a diffusion bar design and placement which encourages turbulent mixing and dispersion of air bubbles more uniformly throughout the sewage. These and other objects will be apparent to those skilled in the art field.